This invention relates to laser diode bars mounted on heat sinks and, more particularly, to avoiding the introduction of defects when soldering laser diode bars to heat sinks.
It is current practice to solder laser diode bars to copper heat sinks, sometimes using an intermediate layer of CuW between the diode bar and the heat sink. Because of the wide angle of emission, it is also current practice to mount the emitting edge of the laser bar at the very edge of the heat sink so that none of the emerging rays are blocked. In the soldering operation, the laser diode bar is placed on a solder preform of AuSn atop the heat sink The assembly is aligned at the emitting edge of the laser bar using a planar datum, clamped together and placed in an oven to reflow the solder Because of the small dimensions involved, the molten solder is liable to flow by capillary action up and over the emitting face of the laser bar, spoiling the light emission from the diode. It would be of great advantage to improve the soldering of laser bars to heat sinks by preventing such unwanted solder overrun.
In accordance with the invention, a laser diode bar, solder preform and heat sink are assembled prior to reflowing the solder in a manner to prevent molten solder from being drawn by capillary action over the light emitting end of the diode bar. A pair of recessed alignment pins 37 establish a datum that locates the emitting end of the laser bar, solder preform and an edge of the heat sink without contacting the emitting surface of the laser bar. Advantageously, the recesses in the alignment pins allow the laser bar and solder preform to overhang the heat sink edge by respective amounts. When molten, the solder will not be drawn by capillary action to obscure the light emitting end of the laser diode bar.